Ballast water is used to balance the weight distribution in a marine vessel. Ballast water is pumped into tanks where it is stored to properly balance a vessel for a voyage. Often ballast water is taken on at one port and transported to another where it is emptied into the new port. This common practice has an inherent danger. Releasing the ballast water taken aboard from a distant location can be both harmful to the environment and dangerous to human and animals in a new port.
The introduction of non-native marine life into a new ecosystem can have a devastating effect on the native flora and fauna which may not have natural defenses to the new species. Additionally, harmful bacterial pathogens, such as cholera, may be present in the origination port. These pathogens can multiply in the ballast tanks over time and cause an outbreak of illness in the area where they are released.
The dangers posed by the marine life and pathogens may be controlled by killing those species present in the ballast water. For the past century, chlorination has become the standard way to disinfect water supplies, potable water, wastewater and swimming pools, for example, to eliminate epidemics of waterborne diseases.